Electronic device for liquid immersion cooling and cooling system using the same

ABSTRACT

An electronic device is immersed in a coolant filled in a cooling apparatus, and directly cooled. The electronic device is configured to be housed in each of housing parts of the cooling apparatus, and includes a metal board held with a pair of board retainers disposed in the housing part, one or more substrate groups attached to a first surface of the metal board and a second surface opposite the first surface, and a plurality of slots disposed above the one or more substrate groups, and arranged onto the metal board in parallel, each of which allows a power unit to be housed. The third circuit board is disposed so that the slots are interposed between the third circuit board and the metal board, and the network cable sockets are arranged in parallel on one side of the third circuit board, located at an opening side of the slots.

TECHNICAL FIELD

The present invention relates to an electronic device, and a coolingsystem using the electronic device. More specifically, the presentinvention relates to an electronic device immersed in the coolant filledin a cooling apparatus so as to be directly cooled, and further relatesto a cooling system using the electronic device. The electronic devicedescribed in the specification is required to exhibit super-highperformance and stable operation while generating high heating value.However, it is not limited to the one as described above.

BACKGROUND ART

Power consumption is one of the essential factors to determine theperformance limit of the recent supercomputer. The importance of studyon saving power consumed by the supercomputer has been widelyrecognized. That is, the speed performance per power consumption(Flops/W) is one of indexes for evaluating the supercomputer. The powerfor cooling operations accounts for approximately 45% of the powerconsumption of the entire data center. Reduction in the powerconsumption by improving cooling efficiency has been increasinglydemanded.

Conventionally, the process for cooling the supercomputer and the datacenter has been performed through two different methods, that is, aircooling method and liquid cooling method. In general, the coolingefficiency of the liquid cooling method is better than that of the aircooling method because of superior heat transfer performance to that ofair. Especially, in comparison with the liquid immersion cooling systemusing synthetic oil, the liquid immersion cooling system usingfluorocarbon-based coolant has received a lot of attention because ofthe advantage in regards to the maintenance work for the electronicdevice (specifically, for example, adjustment, inspection, repair,replacement, extension and the like).

The inventor has already developed the compact liquid immersion coolingapparatus with excellent cooling efficiency suitable for thesupercomputer of small-scale liquid immersion cooling type. Suchapparatus has been applied to the compact supercomputer “Suiren”installed in the high-energy accelerator research organization foroperation (Non-patent Literature 1).

The inventor has also proposed the improved liquid immersion coolingapparatus configured to allow substantial improvement in packagingdensity of the electronic devices subjected to the liquid immersioncooling (Non-patent Literature 2).

CITATION LIST

Non-Patent Literature 1: “Liquid immersion cooling compact supercomputer“ExaScaler-1” succeeded in measurement of the value corresponding to theworld highest level of the latest supercomputer power consumptionperformance ranking “Green500” resulting from the performanceimprovement by 25% or higher” Mar. 31, 2015, Press Release, ExaScalerInc., et al.,URL:http://exascaler.co.jp/wp-content/uploads/2015/03/20150331.pdf

Non-Patent Literature 2: “Innovation of Semiconductor, Cooling,Connection, Aiming at Exa-grade High-performance Machine—Part I”, July2015 issue of Nikkei Electronics, pp. 99-105, Jun. 20, 2015, publishedby Nikkei Business Publications, Inc.

SUMMARY OF INVENTION Technical Problem

There has been required to develop an electronic device applied to theliquid immersion cooling apparatus, which is newly configured to allow aplurality of processors to carry out arithmetic operations as primeobjects so that the packaging density is further increased.

There has also been required to develop an electronic device applied tothe liquid immersion cooling apparatus, which is newly configured tosecure redundancy of the power unit while improving the packagingdensity.

There has been required to develop an electronic device applied to theliquid immersion cooling apparatus, which is newly configured to mainlyoperate a plurality of storage units for storage purposes so as toensure further improvement in the packaging density.

Additionally, there has been required to develop a newly configuredcooling system for directly cooling a plurality of electronic devices ofdifferent types immersed in the coolant filled in the cooling apparatus,which allows arbitrary configuration of the computer with desiredcalculation capacity and desired storage capacity.

Solution to Problem

According to an aspect of the present invention, the electronic devicethat is immersed in a coolant filled in a cooling apparatus, anddirectly cooled is configured to be housed in each of a plurality ofhousing parts of the cooling apparatus. The electronic device includes ametal board held with a pair of board retainers disposed in the housingpart, and one or more substrate groups attached to a first surface ofthe metal board and a second surface opposite the first surface. Thesubstrate group includes one or more first circuit boards, eachincluding a plurality of sockets for mounting a plurality of processorsand main memories on one surface of a substrate, and a component forinterconnecting the processors, a second circuit board including amother board component which includes at least a chipset for controllingthe main memory, but does not include the sockets for mounting theprocessors and the main memories, and the component for interconnectingthe processors, a connector for electrically connecting between the oneor more first circuit boards and the second circuit board, and a flowchannel formed in a gap between a surface opposite the one surface ofthe one or more first circuit boards, and one surface of the secondcircuit board, which faces the surface opposite the one surface of theone or more first circuit boards.

According to another aspect of the present invention, the electronicdevice that is immersed in a coolant filled in a cooling apparatus, anddirectly cooled is configured to be housed in each of a plurality ofhousing parts of the cooling apparatus. The cooling apparatus includes acooling tank with an open space defined by a bottom wall and side walls,a plurality of arranged housing parts formed by dividing the open spaceusing a plurality of internal partition walls in the cooling tank, andan inflow opening and an outflow opening for the coolant. The inflowopening is formed in a bottom part or a side surface of each of thehousing parts, and the outflow opening is formed around a surface of thecoolant circulating in the respective housing parts. The electronicdevice includes a metal board held with a pair of board retainersdisposed in the housing part, and one or more substrate groups attachedto a first surface of the metal board and a second surface opposite thefirst surface. The substrate group includes one or more first circuitboards, each including a plurality of sockets for mounting a pluralityof processors and main memories on one surface of a substrate, and acomponent for interconnecting the processors, a second circuit boardincluding a mother board component which includes at least a chipset forcontrolling the main memory, but does not include the sockets formounting the processors and the main memories, and the component forinterconnecting the processors, a connector for electrically connectingbetween the one or more first circuit boards and the second circuitboard, and a flow channel formed in a gap between a surface opposite theone surface of the one or more first circuit boards, and one surface ofthe second circuit board, which faces the surface opposite the surfaceof the one or more first circuit boards.

In a preferred embodiment of the electronic device according to theaspect of the present invention, the electronic device further includesa plurality of spacers for holding the gap, and a plurality of screws.Each of the screws may be configured to pierce through the first circuitboard, the second circuit board, and the respective spacers forfastening.

In a preferred embodiment of the electronic device according to theaspect of the present invention, the electronic device has a connectedbody formed by attaching the one or more substrate groups respectivelyto the first and the second surfaces of the metal board. Preferably, theconnected body has an external shape similar to an internal shape of thehousing part. For example, the connected body may have a rectangularparallelepiped external shape.

According to another aspect of the present invention, the electronicdevice that is immersed in a coolant filled in a cooling apparatus, anddirectly cooled is configured to be housed in each of a plurality ofhousing parts of the cooling apparatus. The electronic device includes ametal board held with a pair of board retainers disposed in the housingpart, one or more substrate groups attached to a first surface of themetal board and a second surface opposite the first surface, and aplurality of slots disposed above the one or more substrate groups, andarranged onto the metal board in parallel, each of which allows a powerunit to be housed. The substrate group includes a plurality of firstcircuit boards, each including a plurality of sockets for mounting aplurality of processors and main memories on one surface of a substrate,and a component for interconnecting the processors, a second circuitboard including a mother board component which includes at least achipset for controlling the main memory, but does not include thesockets for mounting the processors and the main memories, and thecomponent for interconnecting the processors, a third circuit boardincluding a plurality of network controller chips and a plurality ofnetwork cable sockets corresponding to the respective first circuitboards, a first connector for electrically connecting between the firstcircuit boards and the second circuit board, a second connector forelectrically connecting between the second circuit board and the thirdcircuit board, and a flow channel formed in a gap between a surfaceopposite the one surface of the one or more first circuit boards, andone surface of the second circuit board, which faces the surfaceopposite the one surface of the one or more first circuit boards. Thethird circuit board is disposed so that the slots are interposed betweenthe third circuit board and the metal board, and the network cablesockets are arranged in parallel on one side of the third circuit board,located at an opening side of the slots.

According to another aspect of the present invention, the electronicdevice that is immersed in a coolant filled in a cooling apparatus, anddirectly cooled is configured to be housed in each of a plurality ofhousing parts of the cooling apparatus. The cooling apparatus includes acooling tank with an open space defined by a bottom wall and side walls,a plurality of arranged housing parts formed by dividing the open spaceusing a plurality of internal partition walls in the cooling tank, aninflow opening, and an outflow opening for the coolant. The inflowopening is formed in a bottom part or a side surface of each of thehousing parts, and the outflow opening is formed around a surface of thecoolant circulating in the respective housing parts. The electronicdevice includes a metal board held with a pair of board retainersdisposed in the housing part, one or more substrate groups attached to afirst surface of the metal board and a second surface opposite the firstsurface, and a plurality of slots disposed above the one or moresubstrate groups, and arranged onto the metal board in parallel, each ofwhich allows a power unit to be housed. The substrate group includes aplurality of first circuit boards, each including a plurality of socketsfor mounting a plurality of processors and main memories on one surfaceof a substrate, and a component for interconnecting the processors, asecond circuit board including a mother board component which includesat least a chipset for controlling the main memory, but does not includethe sockets for mounting the processors and the main memories, and thecomponent for interconnecting the processors, a third circuit boardincluding a plurality of network controller chips and a plurality ofnetwork cable sockets corresponding to the respective first circuitboards, a first connector for electrically connecting between each ofthe first circuit boards and the second circuit board, a secondconnector for electrically connecting between the second circuit boardand the third circuit board, and a flow channel formed in a gap betweena surface opposite the one surface of the one or more first circuitboards, and one surface of the second circuit board, which faces thesurface opposite the one surface of the one or more first circuitboards. The third circuit board is disposed so that the slots areinterposed between the third circuit board and the metal board, and thenetwork cable sockets are arranged in parallel on one side of the thirdcircuit board, located at an opening side of the slots.

In a preferred embodiment of the electronic device according to theaspect of the present invention, the electronic device further includesa plurality of spacers for holding the gap, and a plurality of screws.Each of the screws may be configured to pierce through the first circuitboard, the second circuit board, and the respective spacers forfastening.

In a preferred embodiment of the electronic device according to theaspect of the present invention, the electronic device has a connectedbody formed by attaching the one or more substrate groups respectivelyto the first and the second surfaces of the metal board. Preferably, theconnected body has an external shape similar to an internal shape of thehousing part. For example, the connected body may have a rectangularparallelepiped external shape, for example.

According to an aspect of the present invention, the electronic devicethat is immersed in a coolant filled in a cooling apparatus, anddirectly cooled is configured to be housed in each of a plurality ofhousing parts of the cooling apparatus. The electronic device includes ametal board held with a pair of board retainers disposed in the housingpart, a plurality of storage units attached to a first surface of themetal board and a second surface opposite the first surface, and abackplane including a plurality of connectors for electricallyconnecting the respective storage units, which is attached orthogonallyto the first surface of the metal board, and the second surface oppositethe first surface. The metal board includes a primary member and asecondary member. The primary member includes a plurality of cuts formedin a width direction for fixing a plurality of support plates thatsupport the storage units to the primary member. The secondary memberincludes a plurality of pawls which are inserted into a plurality ofslits formed in the backplane, and fixed to the primary member. Thesupport plates include holes for passage of the coolant.

According to another aspect of the present invention, the electronicdevice that is immersed in a coolant filled in a cooling apparatus, anddirectly cooled is configured to be housed in each of a plurality ofhousing parts of the cooling apparatus. The cooling apparatus includes acooling tank with an open space defined by a bottom wall and side walls,the arranged housing parts formed by dividing the open space using aplurality of internal partition walls in the cooling tank, an inflowopening and an outflow opening both for the coolant. The inflow openingis formed in a bottom part or a side surface of each of the housingparts, and the outflow opening is formed around a surface of the coolantcirculating in the respective housing parts. The electronic deviceincludes a metal board held with a pair of board retainers disposed inthe housing part, a plurality of storage units arranged onto a firstsurface of the metal board and a second surface opposite the firstsurface, and a backplane including a plurality of connectors forelectrically connecting the respective storage units, which is attachedorthogonally to the first surface of the metal board, and the secondsurface opposite the first surface. The metal board includes a primarymember and a secondary member. The primary member includes a pluralityof cuts formed in a width direction for fixing a plurality of supportplates that support the storage units to the primary member. Thesecondary member includes a plurality of pawls which are inserted into aplurality of slits formed in the backplane, and fixed to the primarymember. The support plates include holes for passage of the coolant.

In a preferred embodiment of the electronic device according to theaspect of the present invention, the electronic device further includesone or more substrate groups attached to at least one of the firstsurface of the metal board and the second surface. Each of the one ormore substrate groups may include one or more first circuit boards, eachincluding a plurality of sockets for mounting a plurality of processorsand main memories on one surface of a substrate, and a component forinterconnecting the processors, a second circuit board including amother board component which includes at least a chipset for controllingthe main memory, but does not include the sockets for mounting theprocessors and the main memories, and the component for interconnectingthe processors, a connector for electrically connecting between the oneor more first circuit boards and the second circuit board, and a flowchannel formed in a gap between a surface opposite the one surface ofthe one or more first circuit boards, and one surface of the secondcircuit board, which faces the surface opposite the one surface of theone or more first circuit boards.

In a preferred embodiment of the electronic device according to theaspect of the present invention, the electronic device further includesa plurality of spacers for holding the gap, and a plurality of screws.Each of the screws may be configured to pierce through the first circuitboard, the second circuit board, and the respective spacers forfastening.

In a preferred embodiment of the electronic device according to theaspect of the present invention, the electronic device further includesa plurality of slots disposed above the one or more substrate groups,and arranged onto the metal board in parallel, each of which allows apower unit to be housed. Each of the one or more substrate groupsfurther includes a third circuit board including a plurality of networkcontroller chips and a plurality of network cable sockets correspondingto the respective first circuit boards. The third circuit board may bedisposed so that the slots are interposed between the third circuitboard and the metal board, and the network cable sockets are arranged inparallel on one side of the third circuit board, located at an openingside of the slots.

In a preferred embodiment of the electronic device according to theaspect of the present invention, the electronic device has a connectedbody formed by attaching the storage units and the backplanerespectively to the metal board. Preferably, the connected body has anexternal shape similar to an internal shape of the housing part. Forexample, the connected body may have a rectangular parallelepipedexternal shape.

According to an aspect of the present invention, the cooling systemconfigured to directly cool a plurality of electronic devices ofdifferent types immersed in a coolant filled in a cooling apparatusincludes the cooling apparatus including a cooling tank with an openspace defined by a bottom wall and side walls, a plurality of arrangedhousing parts formed by dividing the open space using a plurality ofinternal partition walls in the cooling tank, an inflow opening and anoutflow opening both for the coolant. The inflow opening is formed in abottom part or a side surface of each of the housing parts, and theoutflow opening is formed around a surface of the coolant circulating inthe respective housing parts, and a plurality of electronic devices ofdifferent types, including one or more first electronic devicesconfigured to mainly execute arithmetic operations through a pluralityof processors, and one or more second electronic devices configured tomainly execute storage through a plurality of storage units. One orarbitrary number of the first electronic devices and one or arbitrarynumber of the second electronic devices are separately housed in thehousing parts of the cooling apparatus for forming a computer with adesired calculation capacity and a desired storage capacity.

In a preferred embodiment of the cooling system according to the aspectof the present invention, the first electronic device includes a metalboard held with a pair of board retainers disposed in the housing part,and one or more substrate groups attached to a first surface of themetal board and a second surface opposite the first surface. Thesubstrate group may include one or more first circuit boards, eachincluding a plurality of sockets for mounting a plurality of processorsand main memories on one surface of a substrate, and a component forinterconnecting the processors, a second circuit board including amother board component which includes at least a chipset for controllingthe main memory, but does not include the sockets for mounting theprocessors and the main memories, and the component for interconnectingthe processors, a connector for electrically connecting between the oneor more first circuit boards and the second circuit boards, and a flowchannel formed in a gap between a surface opposite the one surface ofthe one or more first circuit boards, and one surface of the secondcircuit board, which faces the surface opposite the one surface of theone or more first circuit boards.

In a preferred embodiment of the cooling system according to the aspectof the present invention, the first electronic device has a connectedbody formed by attaching the one or more substrate groups respectivelyto the first and the second surfaces of the metal board. Preferably, theconnected body has an external shape similar to an internal shape of thehousing part. For example, the connected body may have a rectangularparallelepiped external shape.

In a preferred embodiment of the cooling system according to the aspectof the present invention, the second electronic device includes a metalboard held with a pair of board retainers disposed in the housing part,a plurality of storage units arranged onto the first surface of themetal board and the second surface opposite the first surface, and abackplane including a plurality of connectors for electricallyconnecting the respective storage units, which is attached orthogonallyto the first surface of the metal board and the second surface oppositethe first surface. The metal board includes a primary member and asecondary member. The primary member includes a plurality of cuts formedin a width direction for fixing a plurality of support plates thatsupport the storage units to the primary member. The secondary memberincludes a plurality of pawls which are inserted into a plurality ofslits formed in the backplane, and fixed to the primary member. Thesupport plates include holes for passage of the coolant.

In a preferred embodiment of the cooling system according to the aspectof the present invention, the second electronic device has a connectedbody formed by attaching the storage units and the backplanerespectively to the metal board. Preferably, the connected body has anexternal shape similar to an internal shape of the housing part. Forexample, the connected body may have a rectangular parallelepipedexternal shape.

The cooling tank having the “open space” described in the specificationincludes the cooling tank with a simple sealing structure sufficient tosecure maintainability of the electronic device. The simple sealingstructure refers to the one that allows the top plate for closing theopen space of the cooling tank to be disposed on the opening of thecooling tank, or the one that allows the top plate to be detachablymounted via the packing or the like.

The above-described and other objects and advantages will be clearlyunderstood in reference to the following explanations of theembodiments. It is to be understood that the embodiments are describedfor exemplifying purposes, and therefore, the present invention is notlimited to those described herein.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a front view of an electronic device according to anembodiment of the present invention.

FIG. 2 is a side view of the electronic device according to theembodiment of the present invention.

FIG. 3 is a plan view of the electronic device according to theembodiment of the present invention.

FIG. 4 is a perspective view of an electronic device according toanother embodiment of the present invention.

FIG. 5 is an assembly diagram showing a part of the electronic deviceaccording to another embodiment of the present invention.

FIG. 6 is a perspective view of an overall structure of a liquidimmersion cooling apparatus.

FIG. 7 is a longitudinal sectional view of the liquid immersion coolingapparatus.

FIG. 8 is a plan view of the liquid immersion cooling apparatus.

FIG. 9 is a perspective view of a structure of an essential part of theliquid immersion cooling apparatus.

FIG. 10 is a lateral sectional view of a structure of the essential partof the liquid immersion cooling apparatus.

FIG. 11 is a longitudinal sectional view of an example of a liftingmechanism of the liquid immersion cooling apparatus.

FIG. 12 is a view schematically showing a structure of a cooling systemaccording to the present invention.

DESCRIPTION OF EMBODIMENTS

Preferred embodiments of the electronic device according to the presentinvention will be described in detail referring to the drawings.

Referring to FIGS. 1 to 3, an electronic device 100 according to anembodiment of the present invention will be described. FIG. 1 is a frontview of the electronic device 100 according to the embodiment of thepresent invention. FIG. 2 is a side view, and FIG. 3 is a plan view ofthe electronic device. The electronic device 100 is immersed in thecoolant filled in a cooling apparatus to be described later so as to bedirectly cooled. It is configured to be housed in each of a plurality ofhousing parts of the cooling apparatus. The electronic device 100includes a metal board 110 that is retained with a pair of boardretainers to be described later, and a substrate group 120, one of whichis attached to a first surface of the metal board 110, and the other isattached to a second surface opposite the first surface.

In the illustrated example, the substrate group 120 constitutes 4 firstcircuit boards 121. Each of the first circuit boards 121 includes aplurality of sockets 126 a, 126 b for mounting 2 processors 124 and 16main memories 125 on one surface of the substrate, and a component (notshown) for interconnecting the 2 processors. Each number of the firstcircuit boards 121, the processors 124, and the main memories 125 is setfor exemplifying purpose. Arbitrary number may be set so long as it isset as a plural. Preferably, Intel Corporation/QPI (QuickPathInterconnect) is used as the component for interconnecting theprocessors.

The substrate group 120 further includes second circuit boards 122 eachhaving a mother board component (not shown). The mother board componentincludes at least a chipset (not shown) for controlling the main memory125, but does not include the sockets 126 a, 126 b for mounting the 2processors 124 and the 16 main memories 125, and the component (notshown) for interconnecting the processors. The mother board componentmay include the PCI Express bus, and the bus switch unit.

The second circuit board 122 includes a first connector 131 forelectrically connecting between the first circuit board 121 and thesecond circuit board 122, and a flow channel 112 formed in the gapbetween the other surface of the first circuit substrate 121 and onesurface of the second circuit board 122, which faces the other surfaceof the first circuit substrate. The substrate group 120 includes aplurality of spacers 128 for retaining the gap, and a plurality ofscrews 129. Each of the screws 129 pierces through the first circuitboard 121, the second circuit board 122, and the spacers 128,respectively for fastening.

The above-structured first circuit board 121 on which the processors 124and the main memories 125 are mounted may be detachably attached to thesecond circuit board 122. It is possible to subject the first circuitboards 121 including the processors 124 and the main memories 125 toadjustment, inspection, repair, replacement, extension and the likeseparately from the second circuit board 122 including the mother boardcomponent, resulting in significantly improved maintainability.

In the case that the second circuit board 122 with the mother boardcomponent includes the component for interconnecting processors, theremay cause the problem of deteriorating signal quality and lowering thespeed owing to communication between the first circuit board 121 and thesecond circuit board 122. In this embodiment, the first circuit board121 having the component for interconnecting processors ensures toeffectively avoid the above-described problem.

The flow channel 127 between the first circuit board 121 and the secondcircuit board 122 allows the coolant circulating through the flowchannel 127 to immediately take heat from the back surface of the firstcircuit board 121 efficiently, on which the processors are mounted, thusimproving the cooling efficiency.

In the case that the single substrate group 120 is attached to the firstsurface and the second surface of the metal board 110 of the electronicdevice 100, respectively, it is preferable to make the external shape ofthe connected body of the metal board 110 and the two substrate groups120 similar to the internal shape of each of the housing parts of thecooling apparatus to be described below. Preferably, the external shapeof the connected body is a rectangular parallelepiped, for example, asshown in the drawing.

Referring to the illustrated example, each of the substrate group 120includes a third circuit board 123. The third circuit board 123 includes4 network controller chips (not shown), and 8 network cable sockets 136,respectively corresponding to the 4 first circuit boards 121. A secondconnector 132 serves to electrically connect between the second circuitboard 122 and the third circuit board 123.

Referring to the illustrated example, 2 slots 134 are attached to thefirst surface, and the second surface opposite the first surface of themetal board 110, respectively above the substrate group 120 parallel tothe metal board 110. As FIG. 3 shows, each of the 4 slots 134 isconfigured to store the power unit 135. The third circuit board 123 isfixed to the metal board 110 using the 2 spacers 138 and the screw 139piercing through the second circuit board 122 so that the 2 slots 134parallel to each other are interposed between the third circuit board123 and the metal board 110. Eight network cable sockets 136 aredisposed in parallel on one side of the third circuit board 123 at theopening side of the 2 slots 134.

A socket of the third connector 133 for electrically connecting thepower unit 135 and the second circuit board 122 is formed in the bottomof each slot. Three bottom holes 137 through which the coolant passesare formed in the bottom of each slot for immediately and efficientlytaking heat from the power unit 135.

As described above, the metal board 110 is combined with the thirdcircuit board 123 having 4 network controller chips (not shown)corresponding to the 4 first circuit boards 121, respectively, and 8network cable sockets 136 arranged on the single side in parallel to oneanother. The combination allows arrangement of the 2 slots 134 for thepower unit 135 between the third circuit board 123 and the metal board110 at the position that cannot be interfered with the network cablesockets 136. Conventionally, as the number of the first circuit boards121 as the CPU units becomes large, it becomes more difficult to securethe space for accommodating 2 or more power units 135 because of theincreased number of the network cable sockets. The use of theabove-described arrangement according to the embodiment ensures to solvethe problem. That is, it is possible to impart redundancy of the powerunit 135 for each of the substrate groups 120.

An electronic device 300 according to another embodiment of the presentinvention will be described referring to FIGS. 4 and 5. FIG. 4 is aperspective view of the electronic device 300 according to anotherembodiment of the present invention, and FIG. 5 is an assembly diagramshowing a part of the electronic device. The electronic device 300 isimmersed in the coolant filled in a cooling apparatus to be describedlater so as to be directly cooled. It is configured to be housed in eachof a plurality of housing parts of the cooling apparatus.

The electronic device 300 includes a metal board 310 that is retainedwith a pair of board retainers provided for the housing part to bedescribed later, and a plurality of HDDs (Hard Disk Drive) 351 which aredisposed on the first surface, and the second surface opposite the firstsurface of the metal board 310, respectively. Referring to theillustrated example, 6 HDDs 351 are disposed on the first surface, and20 HDDs 351 are disposed on the second surface. On the second surface,24 SSDs (Solid State Drive) 352 are disposed. Those HDDs 351 and SSDs352 correspond to a plurality of storage units.

Likewise the electronic device 100 as shown in FIGS. 1 to 3, theelectronic device 300 includes one or more substrate groups 320, eachincluding a first circuit board 321, a second circuit board 322, and athird circuit board 323. Structures of the first circuit board 321, thesecond circuit board 322, and the third circuit board 323 are similar tothose of the first circuit board 121, the second circuit board 122, andthe third circuit board 123, respectively. Structures of the processor324, the main memory 325, the sockets 326 a, 326 b, the power unit 335,and the network cable socket 336 are similar to those of the respectivecomponents of the electronic device 100, respectively. Accordingly,detailed explanations of those structures will be omitted.

In view of high-density mount of a plurality of storage units, theembodiment is characterized by the structure of the metal board 310 andthe structure of the backplane 340 as shown in FIG. 5. The metal board310 includes a plurality of storage connectors 360 for electricallyconnecting the respective storage units. The backplane 340 is attachedat right angles with the first surface and the second surface oppositethe first surface of the metal board 310.

The metal board 310 includes a primary member 311 and a secondary member312. The primary member 311 includes a plurality of cuts 313 each formedin the width direction for fixing a plurality of support plates thatsupport the respective storage units, that is, the HDD support plates315 to the primary member 311. Meanwhile, the secondary member 312includes a plurality of pawls 314 which are inserted into a plurality ofslits 341 formed in the backplane 340, respectively, and fixed to theprimary member 311. Among the support plates, each of the HDD supportplates 315, 316 includes holes for passage of the coolant. In theillustrated example, there are 4 HDD support plates 315 so that 15 (5×3)HDDs 351 may be disposed. There are 3 HDD support plates 316 so that 9(3×3) HDDs 351 may be disposed. Furthermore, there are 2 HDD supportplates 317 so that 2 (1×2) HDDs 351 may be disposed. Meanwhile, it ispossible to dispose 24 (6×4) SSDs 352 by combining the SSD supportplates 318, 319 with the not-shown components.

Upon attachment of the storage units (HDDs 351, SSDs 352), the backplane340, and the substrate group 320 to the metal board 310, the externalshape of the connected body of the metal board 310, the storage units,the backplane 340, and the substrate group 320 may be similar to eachinternal shape of the respective housing parts. The external shape ofthe connected body may be rectangular parallelepiped as shown in FIG. 4.

Detailed explanation will be made with respect to preferred embodimentsof the liquid immersion cooling apparatus configured to immerse theelectronic device 100 according to an embodiment of the above-describedinvention, or the electronic device 300 according to another embodimentin the coolant for direct cooling in reference to the drawings. Thefollowing explanation relates to the high density liquid immersioncooling apparatus configured to house 16 units of the electronic devices100 in the divided housing parts of the cooling tank so as to be cooled.The above explanation is made only for illustrative purpose, and anarbitrary number of units of the electronic devices may be housed withhigh density in the liquid immersion cooling apparatus without limitingthe structure of the electronic device to which the present invention isapplied.

Referring to FIGS. 6 to 11, a liquid immersion cooling apparatus 1according to an embodiment includes a cooling tank 10. An open space 10a is defined by a bottom wall 11 and side walls 12 of the cooling tank10. Inner partitions 13 a, 13 b, 13 c, 13 d, 13 e are laterally disposedin the cooling tank 10 so as to equally divide the open space 10 a into4 arrayed housing parts 14 a, 14 b, 14 c, 14 d. In the embodiment, 4units of a vertically long electronic device 100 having the widthapproximately ¼ of the longitudinal length of the open space 10 a of thecooling tank 10 are housed in each of the housing parts 14 a, 14 b, 14c, 14 d. That is, 16 units of the electronic device may be housed withhigh density.

A casing 12 a is provided around the outer periphery of the side walls12 of the cooling tank 10. The space is formed between the side wall 12at the front side of the cooling tank 10 and the casing 12 a. A topplate 10 b for closing the open space 10 a of the cooling tank 10 may behoused in the space. Upon the maintenance work for the liquid immersioncooling apparatus 1, the top plate 10 b is kept housed in the space.Upon operation of the liquid immersion cooling apparatus 1, the topplate 10 b is taken out from the space to cover the opening of thecooling tank 10 so that the open space 10 a is closed.

The coolant (not shown) is filled in the cooling tank 10 up to theliquid surface (not shown) sufficient to immerse the entire body of theelectronic device 100. It is preferable to use a fluorine based inertliquid formed of the complete fluoride well known as “Fluorinert(trademark of 3M Japan Products Limited) FC-72” (boiling point: 56° C.),“Fluorinert FC-770” (boiling point: 95° C.), “Fluorinert FC-3283”(boiling point 128° C.), “Fluorinert FC-40” (boiling point: 155° C.),“Fluorinert FC-43” (boiling point: 174° C.), all of which aremanufactured by 3M Japan Products Limited. However, the arbitrarycoolant may be used in a nonrestrictive way. The use of Fluorinert FC-40and Fluorinert FC-43 each having the boiling point higher than 150° C.,which hardly evaporates is advantageous for keeping the liquid levelheight in the cooling tank 10 for a long period of time.

Disposed below the bottom wall 11 of the cooling tank 10 are a pluralityof inflow headers 16 each having inlets 15 for the coolant at both ends,and a plurality of outflow headers 17 each having outlets 18 for thecoolant at both ends. Those inflow headers 16 and the outflow headers 17are alternately arranged in the lateral direction with respect to thebottom wall 11 of the cooling tank 10.

Each of the inner partitions 13 a, 13 b, 13 c, 13 d, 13 e includes aplurality of inflow pipes 160, and a plurality of outflow pipes 170 bothpenetrating through the bottom wall 11 via bottom openings 150, andextending to the level around the liquid surface of the coolant, and aplurality of board retainers 130 for retaining an edge of the metalboard 110 of the electronic device 100. In the embodiment, the inflowpipes 160 and the outflow pipes 170 are alternately disposed via supportspacers 140 at left and right sides of the board retainers 130 eachhaving one end fixed to the bottom wall 11. In each of the housing parts14 a, 14 b, 14 c, 14 d, a recess part formed by a pair of boardretainers 130 longitudinally facing with each other in the cooling tank10 is designed to mechanically hold the edge of the metal board 110 ofthe electronic device 100 at both sides. For the mechanical holdingoperation, it is possible to attach a rod-like support to the edge ofthe metal board 110 so as to be fit with the width of the recess partformed by the board retainers 130.

Each of the inflow pipe 160 and the outflow pipe 170 has a rectangularcross section, for example. The inflow pipe 160 has a plurality of smallholes as inflow openings 116 along the longitudinal direction of theinflow pipe 160. Likewise, the outflow pipe 170 has a plurality of smallholes as outflow openings 117 along the longitudinal direction of theoutflow pipe 170. The inflow openings 116 are formed in front and backsurfaces of the inflow pipe 160. Likewise, the outflow openings 117 areformed in front and back surfaces of the outflow pipe 170.

Additionally, a plurality of small holes penetrating through the bottomwall 11 are formed in bottom parts of the housing parts 14 a, 14 b, 14c, 14 d as additional inflow openings 116 and outflow openings 117,respectively. Another outflow opening 127 is formed in the upper portionof the side wall 12 at the back side of the cooling tank 10. The outflowopening 127 formed in the side wall 12 at the back side corresponds tothe outflow opening formed in the part around the liquid surface of thecoolant.

In the embodiment, the circulation of the coolant in the use of theliquid immersion cooling apparatus 1 will be briefly described. The coldcoolant which has been supplied from the inlets 15 at both ends to theinflow header 16 is partially discharged from the inflow openings 116formed in the respective bottom parts of the housing parts 14 a, 14 b,14 c, 14 d. The remaining coolant is supplied into the inflow pipes 160through the bottom openings 150. The coolant supplied into the inflowpipes 160 is discharged from the inflow openings 116 formed in theinflow pipes 160.

The coolant warmed by heat taken from the electronic devices 100 housedin the housing parts 14 a, 14 b, 14 c, 14 d passes through the outflowopening 127 formed in the side wall 12 at the back side of the coolingtank 10 at the height near the liquid surface, and flows out of thecooling tank 10. The warmed coolant is partially drawn into the outflowheaders 17 from the outflow openings 117 formed in the bottom parts ofthe housing parts 14 a, 14 b, 14 c, 14 d. At the same time, the coolantpasses through the outflow openings 117 formed in the outflow pipe 170,and the bottom openings 150 so as to be drawn into the outflow headers17. The coolant drawn into the outflow headers 17 flows out of thecooling tank 10 while passing through the outlets 18.

The inflow openings 116 for the coolant are formed in the bottom partsor the side surfaces of the respective housing parts 14 a, 14 b, 14 c,14 d, and the outflow opening 127 is formed around the liquid surface ofthe coolant. The above-described structure prevents stagnation of thecoolant which has been warmed by the highly densely housed electronicdevices 100 in the respective housing parts 14 a, 14 b, 14 c, 14 d sothat the cooling efficiency is improved. The structure having the inflowpipe 160 with the inflow openings 116 and the outflow pipe 170 with theoutflow openings 117 disposed at the left and right sides of each of theboard retainers 130 alternately via the support spacers 140 isespecially advantageous because of further enhanced effect of preventingthe coolant stagnation.

Referring to the drawing, the detailed explanation will be made withrespect to the lifting mechanism configured to lift and lower thevertically long electronic devices 100 which are highly densely housedin the cooling tank 10 from/into the housing parts 14 a, 14 b, 14 c, 14d, respectively.

A lifting mechanism 20 includes an arm 22 configured to lift theelectronic devices 100 from the housing parts 14 a, 14 b, 14 c, 14 d,and lower them into the housing parts 14 a, 14 b, 14 c, 14 d. Thelifting mechanism 20 includes a tower 21 equipped with a guide 218 and amotive power source 213 for raising and lowering the arm 22, and a slidemechanism 23 attached to the cooling tank 10 for movably supporting thetower 21 relative to the cooling tank 10 in a horizontal plane locatedabove the open space 10 a. As the slide mechanism 23 is directlyattached to the cooling tank 10, the stage does not have to be providedin the periphery of the installation surface of the cooling tank 10. Theguide 218 and the motive power source 213 of the tower 21 allow the arm22 to move up and down. This makes it possible to safely lift or lowerthe electronic devices housed with high density in the cooling tankwithout vibrating the arm forward, backward, leftward, and rightwardduring the lifting operation.

In the embodiment, the tower 21 includes a reducer 214 for reducing therotating speed of a shaft of the motive power source 213 such as theservo motor, a gear 215 for converting the rotary motion of the shaft ofthe reducer 214 into the rotary motion of the shaft orthogonal to theshaft of the reducer 214, a pair of timing pulleys 216, and a timingbelt 217. One of brackets 222 of the arm 22 is movably supported at theguide 218 disposed in the vertical direction (Z direction) via a guideroller 219. The other bracket 222 of the arm 22 is fixed to the timingbelt 217 through a belt holder 220. The shaft of the gear 215 and theshaft of the timing pulley 216 are rotatably supported with bearingholders 223.

In the embodiment, the slide mechanism 23 includes a pair oflongitudinal rails 24 disposed on top ends of the pair of side walls 12positioned in the width direction of the cooling tank 10, a movable base25 movably supported on the pair of longitudinal rails 24, and a pair oflateral rails 26 disposed on the movable base 25. The tower 21 ismovably supported on the pair of lateral rails 26. Specifically, aplurality of guide rollers 251 attached to the lower part of the movablebase 25 slide on the pair of longitudinal rails 24 so as to allow thelongitudinal movement (Y direction) of the tower 21. The guide rollers251 attached to a fixation base 211 at the bottom part of the tower 21slide on the pair of lateral rails 26 to allow the lateral movement (Xdirection) of the tower 21.

Referring to the example shown in the drawing, a pair of supports 28 areused for placing the pair of longitudinal rails 24 on the top ends ofthe side walls 12 of the cooling tank 10. The support 28 is fixed to thetop end of the side wall 12 so that one end of the support 28 projectsrearward of the cooling tank 10 by the length substantially equal to thelongitudinal length of the tower 21. The pair of longitudinal rails 24are disposed on the thus projected pair of supports 28. Then the pair oflongitudinal rails 24 have running ranges where the movable bases 25 arelocated at the position apart from the rear of the upper part of theopen space 10 a of the cooling tank 10 for allowing the electronicdevice 100 to be lifted from the housing part 14 a that is the nearestto the side wall 12 at the back surface side of the cooling tank 10, andto be lowered into the housing part 14 a. The pair of supports 28 andthe pair of longitudinal rails 24 are disposed so as to be locatedoutside the width of the top plate 10 b when it is disposed to cover theopening of the cooling tank 10. The above-described structure isdesigned so that those supports 28 and the longitudinal rails 24 do notinterfere with covering of the open space 10 a by the top plate 10 b.

Stoppers 27 disposed in the periphery of both ends of the pair oflongitudinal rails 24 serve to restrict the range in which the tower 21moves in the longitudinal direction (Y direction) of the cooling tank 10in a horizontal plane located above the open space 10 a. The stoppers 27disposed in the periphery of both ends of the pair of lateral rails 26serve to restrict the movement of the tower 21 so that the range inwhich the tower 21 moves in the width direction (X direction) of thecooling tank 10 does not substantially exceed at least the width of theopen space 10 a. This ensures to prevent the fixation base 211 or ahousing 212 of the tower 21 from extending over the width of the coolingtank 10 upon movement of the tower 21 in the width direction of thecooling tank 10. Although the plurality of liquid immersion coolingapparatuses are densely arranged, the above-described structure mayprevent the interference between operation ranges of the liftingmechanisms of the adjacent liquid immersion cooling apparatuses.

The operation of the above-structured lifting mechanism 20 will bedescribed. The tower 21 is horizontally moved with a handle at the sideof the tower 21, and stopped at the position where the arm 22 is locatedjust above the metal board 110 of the electronic device 100 to belifted. A controller (not shown) is operated to drive the motive powersource 213 of the tower 21 so that the rotation of the shaft of themotive power source 213 is transferred to the timing pulley 216 via thegear 215 to lower the arm 22 to the lowermost part. In this state, tipsof a pair of suspension fittings 221 attached to the lower part of thearm 22 are connected to a pair of holes formed in the top end of themetal board 110 of the electronic device 100. Then the controller (notshown) is operated to transfer the reverse rotation of the shaft of themotive power source 213 of the tower 21 to the timing pulley 216 forlifting the arm 22. The electronic device 100 which is suspended withthe arm 22 by the suspension fittings 221 is then lifted while havingthe metal board 110 sliding in the board retainer 130. Upon raising ofthe arm 22 to the uppermost part, the electronic device 100 is broughtinto the suspended state while being completely taken out from the boardretainer 130 of the housing part 14 a, 14 b, 14 c, or 14 d. In theabove-described state, the tower 21 may be horizontally moved to conductthe maintenance work for the electronic device 100 as needed. Afterfinishing the maintenance work, the controller (not shown) is operatedagain to lower the electronic device 100 into the housing part 14 a, 14b, 14 c, or 14 d so as to be returned to the original position.

Meanwhile, the controller (not shown) is operated to stop the drivingoperation of the motive power source 213 of the tower 21 in the processof lifting or lowering the arm 22 so that the arm 22 is made stationaryat the arbitrary height in the vertical direction of the tower 21. Theelectronic device 100 is suspended at the desired height while beingheld partially in the board retainer 130 of the housing part 14 a, 14 b,14 c, or 14 d without being completely taken out therefrom. In theabove-described state, it is possible to conduct the maintenance workfor the electronic device 100. In the state where the electronic device100 is suspended as well as in the stationary state at the arbitraryheight in the direction vertical to the tower 21, the reducer 214 helpsin preventing the downward load applied to the arm 22 from causingunintentional rotation of the shafts of the timing pulley 216 and themotive power source 213.

In the above embodiment, the use of the single cooling tank has beenexplained as an example. However, it is possible to employ a pluralityof cooling tanks adjacently arranged in the lateral direction. In thiscase, at least one lifting mechanism may be shared by the adjacentlydisposed cooling tanks. Specifically, the at least one lifting mechanismmay be configured to include the tower having the guide and the motivepower source for raising and lowering the arm, the slide mechanism whichis attached to the adjacent cooling tank for movably supporting thetower relative to the adjacent cooling tank in a horizontal planelocated above the open space, and the stoppers for restricting movementof the tower so that the tower movement range in the width direction ofthe adjacent cooling tank does not substantially exceed the distancebetween the side walls separated farthest in the lateral direction amongthose for forming the open space between the adjacent cooling tanks.

In the case of the plurality of cooling tanks adjacently arranged in thelateral direction, preferably, the slide mechanism includes the pair oflongitudinal rails disposed on top ends of the pair of side wallslocated in the width direction of the respective cooling tanks, themovable bases supported movably on the pair of longitudinal rails, andthe pair of lateral rails disposed on the movable bases. Preferably, thetower is movably supported on the pair of lateral rails. The width ofthe movable base may be substantially the same as that of the coolingtank, or the same as the whole width of the adjacently arranged coolingtanks. If the movable base has the width substantially the same as thatof the single cooling tank, the pair of lateral rails for one of theadjacent cooling tanks may be linked to the pair of lateral rails forthe other cooling tank using the appropriate linkage member. This makesit possible to move the tower on one pair of lateral rails onto theother pair of lateral rails so that the single tower is shared by theadjacently arranged cooling tanks. If the movable base has the widthsubstantially the same as the whole width of a plurality of adjacentlyarranged cooling tanks, the length of the pair of lateral rails may beset to the whole width of the adjacently arranged cooling tanks.Therefore, the linkage member for linking the pairs of lateral rails isnot required.

In the above embodiment, the manual movement of the tower 21 in thehorizontal plane has been explained as an example. It is possible to adda motive power source for running the movable base 25 on thelongitudinal rail 24, and another motive power source for running thetower 21 including the fixation base 211 on the lateral rail 26 to thelifting mechanism so as to move the tower 21 by operation of thecontroller (not shown). It is possible to employ the electric motivepower source such as servo motor for those additional motive powersources.

In the case of movement of the tower 21 in the horizontal plane byadding the electric motive power sources, it is preferable to replacethe mechanical stoppers 27 as shown in the drawing for physicallypreventing movement of the tower 21 with the movement restrictionmechanism through software. In the specification, the stopper mayinclude both the mechanical stopper and the movement restrictionmechanism through software.

The liquid immersion cooling apparatus according to the embodimentensures to safely lift and lower the electronic device housed in thecooling tank with high density without requiring the stage in theperiphery of the installation surface of the cooling tank. Additionally,dense arrangement of a plurality of liquid immersion cooling apparatusesprevents mutual interference between the movement ranges of the liftingmechanisms of adjacent liquid immersion cooling apparatuses.

As described above, in the embodiment, it is possible to house aplurality of different kinds of electronic devices including theelectronic devices 100 and 300, for example, in the plurality of housingparts in the cooling tank without being limited to the case where theelectronic devices of the single type are housed. In other words, aplurality of different kinds of electronic devices include one or morefirst electronic devices each configured to mainly execute arithmeticoperations through a plurality of processors, and one or more secondelectronic devices each configured to mainly store data through aplurality of storage units. One or arbitrary number of the firstelectronic devices and one or arbitrary number of the second electronicdevices are housed in the respective housing parts of the coolingapparatus separately so that the cooling system constitutes the computerwith desired calculation capacity and desired storage capacity.Referring to the schematic view in FIG. 12, specifically, FIG. 12(a), 2units of the electronic device 100 and 1 unit of the electronic device300 may be housed in 3 of 16 housing parts of the liquid immersioncooling apparatus 1 to constitute the computer. Referring to FIG. 12(b),6 units of the electronic device 100 and 3 units of the electronicdevice 300 may be housed in 9 housing parts to constitute the computer.The electronic device 100 corresponds to the first electronic device inwhich the arithmetic operation is mainly executed by the processors. Theelectronic device 300 corresponds to the second electronic device inwhich data storage is mainly executed by the storage units.

As described above, arbitrary combination of the first and the secondelectronic devices ensures to constitute the computer with desiredcalculation capacity and desired storage capacity. Therefore, it ispossible to provide the configurable cooling system.

INDUSTRIAL APPLICABILITY

The present invention is widely applicable to electronic devices mountedwith ultra-high density for liquid immersion cooling, and the liquidimmersion cooling system configured to immerse the electronic devices inthe coolant so as to be efficiently cooled.

REFERENCE SIGNS LIST

-   -   1: liquid immersion cooling apparatus,    -   2: cooling system,    -   10: cooling tank,    -   10 a: open space,    -   10 b: top plate,    -   11: bottom wall,    -   12: side wall,    -   12 a: casing,    -   100, 300: electronic device,    -   110, 310: metal board,    -   111: suspension fitting hole    -   112: flow channel,    -   120, 320: substrate group    -   121, 321: first circuit board,    -   122, 322; second circuit board,    -   123, 323: third circuit board,    -   124, 324: processor,    -   125, 325: main memory    -   126 a, 126 b, 326 a, 326 b: socket,    -   128, 138: spacer,    -   129, 139: screw,    -   130: board retainer,    -   131: first connector,    -   132: second connector,    -   133: third connector,    -   134: slot,    -   135, 335: power unit,    -   136, 336: network cable socket,    -   137: bottom hole    -   140: support spacer,    -   13 a, 13 b, 13 c, 13 d, 13 e: inner partition,    -   14 a, 14 b, 14 c, 14 d: housing part,    -   15: inlet,    -   150: bottom opening,    -   16: inflow header,    -   116: inflow opening,    -   160: inflow pipe,    -   17: outflow header,    -   117,127: outflow opening,    -   170: outflow pipe,    -   18: outlet,    -   20: lifting mechanism,    -   21: tower,    -   211: fixation base,    -   212: housing,    -   213: motive power source,    -   214: reducer,    -   215: gear,    -   216: timing pulley,    -   217: timing belt,    -   218: guide,    -   219: guide roller,    -   220: belt holder,    -   22: arm,    -   221: suspension fitting,    -   222: bracket,    -   223: bearing holder,    -   23: slide mechanism,    -   24: longitudinal rail (Y direction),    -   25: movable base,    -   251: guide roller,    -   26: lateral rail (X direction),    -   27: stopper,    -   28: support,    -   311: primary member,    -   312: secondary member,    -   313: cut,    -   314: pawl,    -   315, 316, 317: HDD support plate,    -   318, 319: SSD support plate,    -   340: backplane,    -   341: slit,    -   351: HDD,    -   352: SSD,    -   360: storage connector

The invention claimed is:
 1. An electronic device that is immersed in acoolant filled in a cooling apparatus, and directly cooled, theelectronic device being configured to be housed in each of a pluralityof housing parts of the cooling apparatus, the electronic devicecomprising: a metal board held with a pair of board retainers disposedin the housing part; one or more substrate groups attached to a firstsurface of the metal board and a second surface opposite the firstsurface; and a plurality of slots disposed above the one or moresubstrate groups, and arranged onto the metal board in parallel, each ofwhich allows a power unit to be housed, wherein: the substrate groupincludes a plurality of first circuit boards, each including a pluralityof sockets for mounting a plurality of processors and a main memory onone surface of a substrate, and a component for interconnecting theprocessors, a second circuit board including a mother board componentwhich includes at least a chipset for controlling the main memory, butdoes not include the sockets for mounting the processors and the mainmemory, and the component for interconnecting the processors, a thirdcircuit board including a plurality of network controller chips and aplurality of network cable sockets corresponding to the respective firstcircuit boards, a first connector for electrically connecting betweenthe first circuit boards and the second circuit board, a secondconnector for electrically connecting between the second circuit boardand the third circuit board, and a flow channel formed in a gap betweena surface opposite the one surface of the one or more first circuitboards, and one surface of the second circuit board, which faces thesurface opposite the one surface of the one or more first circuitboards, and the third circuit board is disposed so that the slots areinterposed between the third circuit board and the metal board, and thenetwork cable sockets are arranged in parallel on one side of the thirdcircuit board, located at an opening side of the slots.
 2. An electronicdevice that is immersed in a coolant filled in a cooling apparatus, anddirectly cooled, the electronic device being configured to be housed ineach of a plurality of housing parts of the cooling apparatus, thecooling apparatus including a cooling tank with an open space defined bya bottom wall and side walls, a plurality of arranged housing partsformed by dividing the open space using a plurality of internalpartition walls in the cooling tank, and an inflow opening and anoutflow opening for the coolant, the inflow opening being formed in abottom part or a side surface of each of the housing parts, and theoutflow opening being formed around a surface of the coolant circulatingin the respective housing parts, wherein: the electronic device includesa metal board held with a pair of board retainers disposed in thehousing part, one or more substrate groups attached to a first surfaceof the metal board and a second surface opposite the first surface, anda plurality of slots disposed above the one or more substrate groups,and arranged onto the metal board in parallel, each of which allows apower unit to be housed; the substrate group includes a plurality offirst circuit boards, each including a plurality of sockets for mountinga plurality of processors and a main memory on one surface of asubstrate, and a component for interconnecting the processors, a secondcircuit board including a mother board component which includes at leasta chipset for controlling the main memory, but does not include thesockets for mounting the processors and the main memory, and thecomponent for interconnecting the processors, a third circuit boardincluding a plurality of network controller chips and a plurality ofnetwork cable sockets corresponding to the respective first circuitboards, a first connector for electrically connecting between each ofthe first circuit boards and the second circuit board, a secondconnector for electrically connecting between the second circuit boardand the third circuit board, and a flow channel formed in a gap betweena surface opposite the one surface of the one or more first circuitboards, and one surface of the second circuit board, which faces thesurface opposite the one surface of the one or more first circuitboards, and the third circuit board is disposed so that the slots areinterposed between the third circuit board and the metal board, and thenetwork cable sockets are arranged in parallel on one side of the thirdcircuit board, located at an opening side of the slots.
 3. Theelectronic device according to claim 1, further comprising a pluralityof spacers for holding the gap, and a plurality of screws, wherein eachof the screws pierces through the first circuit board, the secondcircuit board, and the respective spacers for fastening.
 4. Theelectronic device according to claim 1, wherein an external shape of aconnected body formed by attaching the one or more substrate groupsrespectively to the first and the second surfaces of the metal board issimilar to an internal shape of each of the housing parts.
 5. Theelectronic device according to claim 4, wherein the connected body has arectangular parallelpiped external shape.
 6. The electronic deviceaccording to claim 2, further comprising a plurality of spacers forholding the gap, and a plurality of screws, wherein each of the screwspierces through the first circuit board, the second circuit board, andthe respective spacers for fastening.
 7. The electronic device accordingto claim 2, wherein an external shape of a connected body formed byattaching the one or more substrate groups respectively to the first andthe second surfaces of the metal board is similar to an internal shapeof each of the housing parts.
 8. The electronic device according toclaim 7, wherein the connected body has a rectangular parallelpipedexternal shape.